Open-hearth furnace operation



March 12, 1946. R. s. A. DoUGHl-:RTY rA| V2,396,461

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- #M ww@ Patented Mar. 12, 1946- v UNITED STATES. PATENT oi-Flcizj- OPEN-HEARTH FURNACE OPERATION Robert S. A. Dougherty and John E. Eberhardt, Bethlehem, Pa., assignors to Bethlehem Steel Company, a corporation of Pennsylvania Application February 25, 1944, Serial No. 523,862

2 Claims.

This invention relates in general to a method of increasing the production of an open-hearth furnace, and more particularly' tol a method of reducing heat time by the direct firing of the heaters which furnish preheated air to the fur-l nace.

In the manufacture of steel, for example, by the basic open-hearth process, a cold charge of limestone, ore, and scrap is heated 'in the furnace until the scrap has started to melt. A charge of molten pig iron is then added and the melting continues until the charge is completely molten whereupon the limestone rises and iloats on the surface ofthe molten metal forming the refining slag. Jets of burning gas, oil, or other fuel projected alternately from one and then the other end of the furnace impart heat to the charge and to the resulting bath. The hot waste gases pass from the temporarily non-firing end into air preheaters which absorb some of their heat, and thence pass out through a stack. After a brief interval, usually fifteen or twenty minutes, the

temperatures during the course of a heat under the prior practice and Fig. 5 is a chart showing the comparative temperatures of the arches over the slag pocketsmotor-driven blower Il. At their outer ends air.

preheaters 5 and 6 connect through the large ilues I8 and I9 to the central flue 2li and thence to the stack 2|. The central flue 20 and stack 2| may be closed o 'as desired lby the dampers fuel and air are shut oi at the one end, and the gas and air, or air alone, introduced through the air preheater at the Oppsite end. A s'eries of such reversals is continued until puriilcation is completed.

At the end of the heat however, after the rened metal has been tapped, it is necessary to renew'the bottom and recharge the furnace. The doors must stand open for a rather considerable period, admitting cold air to the furnace and thence to the air preheaters by suction. The cold air so drawn in may cause the temperature of the air preheaters todrop as -much as 300 F., and as much as six hours of 'furnace firing may be required to regain the lost temperature.

One object of this invention is a method of raising production and decreasing heat time by burning fuel in the air preheaters during periods of normally lowered temperatures.

A further object is a method of supplying uniformly preheated air to an open-hearth furnace.

Other objects and purposes of this invention will appear hereinafter in the specification and in the vappended claims.

Referring to the drawings:

Figure l is a front elevation of the tapping side of an open-hearth furnace illustrating an application of the invention;

Fig. 2 is a vertical section taken along the lines 2-2 of Fig. 3;

Fig. 3 is a plan view partly in section of the air preheating system of an open hearth furnace;

Fig. 4 is a chart showing typical uptake wall 22 and 23, and the air inlets 24 and 25, provided with dampers 26 and 21, connect to the fiues IB and I9.

The Aair preheaters 5 and 6 are divided into separate chambers by the partition walls 28`and 29, and are provided with short fanlike entrance lues or fantails 3l! and 3I, as in theusual construction.

The method of operation is as follows: Referring to Fig. 3 of the drawings, and assuming that the furnace is in the last or refining stage of a heat, with the burners II and I2 shut off, the

right-hand air preheater 5 having just been heated and the left-hand air preheater 6 being about to be heated,. the cold air from outside enters the air inlet 24 and flows through the open damper 26 and flue I8 to said right-hand preheater 5 where the air is preheated. Thence it passes through the fantails 30,' slag pocket 5 and uptake l and burns the fuel from burner 3 over the hearth 2.; The waste gases of combustion pass through the,vertical flue 8 and fantails 3| into the left-hand preheater 6, and finally l through the flue I9 and open damper 23 to the stack 2I. As an alternative where it is desired to utilize the residual heat of the waste gases,

A the outflow may go to a lconventional waste heat boiler, auxiliary air preheaters, or lthe .like instead of direct to stack.`

not mem on the amsn an been tapped. and

charge lare bound to be cold, and their to cause a sudden drop in the temperapreheaters, which prolonge the and postpones and lengthens the the drawings shows the variation in thetemperatureofanuptakeduringtheprogress of a heat as observed for the prior practice. It be seen that during the greater portion of the heat this temperature exhibits rather regular variations over about half-hour intervals. The correspond to the reversals of the furnace; during a 15 minute interval the temperature falls,

succeeding l minute interval the temperature rises, indicating that the air preheater on that sse . temperature has fallen about 300 F. Furthermore during the balance of the bottom-making and charging period the 'temperature rises very slowly. After the furnace has been charged and during the melting period it will be seen that the median temperature rises until it reaches its maximum value shortly before the end of the melting period and thereafter remains nearly constant throughoutthe refining period or until the heat is tapped. It will be obvious from Fia. 4 thatthemediantemperaturewaslessthanits maximum value for a periocf of about six hours during the making of the heat.

Our invention is directed'toward increasing the air preheaters during the bottom-making and chargingstagesbymeans of the burners Il and i2, which are provided with reversing mechanisms (not shown) so that the proper burner fires into the slag pocket on the outgoing end of the furnace. The blower I1 supplies air to the burners Il and I2 through the pipe lines il and it in sequence, the direction of flow being cony sighted on the arch over-the slag pocket of an rateofheattransfertothechargeduringthis' Aheaters during the bottom-making and chargingstagesoftheheattomaintainasubstantially uniform median temperature during the charging, melting.` and refining stages of the heat. .The resulting higher temperature of the preheated airduringtheperiodwhenthistemperatureis normallylow.asthowninlig.4,resultsinhigher open-hearth furnace are shown in Fig. 5. The lower dashed line indicates temperatures recorded during the making of a heat by the prior practice. It will be seen that the median temperature, indicated by the heavy dashed line,

lshowsthe same sudden drop and gradual rise exhibited in Rig. 4 although the recorded temperatures at corresponding stages of the heat are lower because of the different point at which the temperatures were measured. The upper solid line indicates temperatures recorded during the making of a heat by the new practice. It will be noted that the median temperature, as indicated by the heavy solid line. does not drop but rather .remains substantially konstant throughout the heat. The resulting saving in heat time of about an hour is indicated in l'ig. 5 by the termination of the solid line about an hour before the termination of the dashed line.

While we have thus shown and described our invention in a particular application and embodiment,we wish it understood that other and equivalent applications and embodiments are possible and may be used without departing from the spirit and essence of our invention.

Having thus described our invention, what we claim as new and useful and desire to protect by Letters Patent is:

-l. In an open-hearth'furnace operation, the

steps of heating the air preheaters by the waste gasesofthefurnace,andburningfuelintheair preheaters during the bottom-making and charging stages tomaintain a substantially constant median temperature of the air preheaters during the charging. melting and renning stages- 2. In an open-hearth furnace operation, the step of burning fuel in the air preheaters during the bottom-making and charging stages in suftlcient amount to maintain the temperature of theairpreheatersduringthechargingandmeltllame temperature in the furnace and therefore `ing stages, at substantially as high a temperature as that duringgthe refining stage.

inahigherrateofheattransfertothecharge and an increased production'rete.

Referringagaintorig.8,weburnfuelinthe 

